Asphalt roofing systems and products generally comprise a fiberglass or organic matting, which is filled or coated with various asphalt materials. Generally, the matting is filled with a saturant asphalt that is oil-rich and relatively non-viscous. The saturant asphalt serves as a preservative, a waterproofing agent and an adhesive agent. The saturated substrate may be sealed by application of a harder, more viscous coating asphalt to one or both sides of the substrate. Coating asphalts typically contain finely divided minerals therein as stabilizers or fillers. Such compounds as igneous rock mineral fines, silica, slate dust, talc, micaceous materials, limestone and dolomite have been utilized as fillers to render the coating asphalt more shatter-proof and shock-proof in cold weather.
The exterior, outer, or exposed surface of asphalt roofing systems and products is generally provided with a covering of granular material or roofing granules embedded in the coating asphalt. The granular material generally protects the underlying asphalt coating from damage due to exposure to light, in particular ultraviolet (UV) light. That is, the granules reflect light and protect the asphalt from deterioration by photodegradation. In addition, such granular material improves fire resistance and weathering characteristics. Further, colors or mixtures of colors of granular material may be selected for aesthetics.
In general, the mineral materials, particles or granules are embedded into the coating asphalt under pressure and are retained therein by adherence to the asphalt. With respect to each granule, the asphalt may be viewed as a “hot sticky mud” into which the granules are pressed. When the asphalt cools, pockets having the granules retained therein are formed.
Good adherence of the roofing granules to the roofing product is beneficial. Loss of granules reduces the life of the roof, since it is associated with acceleration of photodegradation of the asphalt. In addition, the aesthetics of the roofing system may be compromised if granules are lost. Further, reduction of granule loss during installation improves safety conditions on the roof.
The granule may be coated with a variety of materials, to render unique and desirable properties. By way of example, the granules may be coated with an oil or a synthetic polymer for purposes of dust suppression or agglomeration. By way of further example, granules are generally treated with an adhesion promoter. Typically, the adhesion promoter has been polyalkylsiloxane, which makes the surface of the coated granule hydrophobic for better wetting with asphalt. This treatment reduces the ingress of water at the granule-asphalt interface, improving the adhesion. When polyalkylsiloxane surface treatments are used, the adhesion at the granule-asphalt interface is dominated by van der Waals interactions.